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<head>
    <meta charset="UTF-8">
    <title>变量</title>
    <link rel="stylesheet" href="style.css">
    <link rel="stylesheet" href="../../jsfile/layer.css"/>
    <script src="../../jsfile/jquery.js"></script>
    <script src="../../jsfile/layer.js"></script>
    <script src="../../jsfile/base.js"></script>
    <script>
        var i;
        // alert(i);//undefined
        i = 12;
        i = "abc";
        //他可以取变量的类型进行返回
        alert(typeof i);

        var a = 12;
        var b = "abc";

        alert(a * b);//NaN  Not a Number    是非数字,非数值

    </script>
</head>
<body>
<p id="text_show">
    变量的使用<br>
    typeof()是javascript语言提供的一个函数<br/>
    javascript是弱类型语言,根据变量的数据类型而改变
</p>
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